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(#) `addJavascriptInterface` Called

!!! WARNING: `addJavascriptInterface` Called
   This is a warning.

Id
:   `AddJavascriptInterface`
Summary
:   `addJavascriptInterface` Called
Severity
:   Warning
Category
:   Security
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   Initial
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://developer.android.com/reference/android/webkit/WebView.html#addJavascriptInterface(java.lang.Object,%20java.lang.String)
See
:   https://support.google.com/faqs/answer/9095419?hl=en
See
:   https://goo.gle/AddJavascriptInterface
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/AddJavascriptInterfaceDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AddJavascriptInterfaceDetectorTest.kt)
Copyright Year
:   2014

For applications built for API levels below 17,
`WebView#addJavascriptInterface` presents a security hazard as
JavaScript on the target web page has the ability to use reflection to
access the injected object's public fields and thus manipulate the host
application in unintended ways.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/AddJavascriptInterfaceTest.java:16:Warning:
WebView.addJavascriptInterface should not be called with minSdkVersion <
17 for security reasons: JavaScript can use reflection to manipulate
application [AddJavascriptInterface]
    webView.addJavascriptInterface(object, string);
            ----------------------
src/test/pkg/AddJavascriptInterfaceTest.java:23:Warning:
WebView.addJavascriptInterface should not be called with minSdkVersion <
17 for security reasons: JavaScript can use reflection to manipulate
application [AddJavascriptInterface]
    webView.addJavascriptInterface(object, string);
            ----------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test/pkg/AddJavascriptInterfaceTest.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.webkit.WebView;
import android.content.Context;

@SuppressWarnings({"ClassNameDiffersFromFileName", "MethodMayBeStatic"})
public class AddJavascriptInterfaceTest {
    private static class WebViewChild extends WebView {
        WebViewChild(Context context) {
            super(context);
        }
    }

    private static class CallAddJavascriptInterfaceOnWebView {
        public void addJavascriptInterfaceToWebView(WebView webView, Object object, String string) {
            webView.addJavascriptInterface(object, string);
        }
    }

    private static class CallAddJavascriptInterfaceOnWebViewChild {
        public void addJavascriptInterfaceToWebViewChild(
            WebViewChild webView, Object object, String string) {
            webView.addJavascriptInterface(object, string);
        }
    }

    private static class NonWebView {
        public void addJavascriptInterface(Object object, String string) { }
    }

    private static class CallAddJavascriptInterfaceOnNonWebView {
        public void addJavascriptInterfaceToNonWebView(
            NonWebView webView, Object object, String string) {
            webView.addJavascriptInterface(object, string);
        }
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AddJavascriptInterfaceDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `AddJavascriptInterfaceDetector.test`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("AddJavascriptInterface")
  fun method() {
     addJavascriptInterface(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("AddJavascriptInterface")
  void method() {
     addJavascriptInterface(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection AddJavascriptInterface
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="AddJavascriptInterface" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'AddJavascriptInterface'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore AddJavascriptInterface ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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